GB2262316A - Piston and cylinder arrangement with reversing valve disposed in the piston. - Google Patents

Abstract

Fluid under pressure supplied to a hollow chamber (5) in a piston head (4) is fed successively to opposite cylinder spaces (13, 14) having bleed holes (11, 12). The piston head (4) is provided with a first bore providing communication between the chamber (5) and the first space (13) and a second bore providing communication between the chamber (5) and the second space (14), the first and second bores having valve seats (15, 16) on their end regions facing the chamber and being larger than the bleed holes (11, 12). A resiliently flexible valve member (18) co-operates with the first and second valve seats (15, 16) so as successively to block off the first and second bores respectively. An elongate element (21) carries the valve member (18) and has first and second end regions (22, 23) projecting through the opposing faces of the piston head (4) into the first and second spaces (13, 14). In use, fluid supplied to the chamber (5) is switched from one space to the other when the elongate member (21) is struck by a respective cylinder end (8, 9). The resilience of the valve member allows it to store some energy so that when triggered, it can move independently of the initial switching force on the "load and fire" principle. <IMAGE>

Description

A PISTON AND CYLINDER ARRANGEMENT WITH ITS OWN CONTROL VALVE MECHANISM This invention relates to a piston and cylinder arrangement with its own valve for controlling the operation of the piston and cylinder arrangement. More particularly, but not exclusively, the present invention relates to a hydraulic cylinder and piston arrangement and its associated control valve, but it is to be appreciated that the piston and cylinder arrangement of the present invention can be driven by any fluid under pressure; however, where the valve is used to control a piston and cylinder arrangement forming part of the mechanism for advancing components of a tank washer, it is convenient for water to be supplied under pressure to the valve. In such an arrangement the piston can be fixed and the cylinder can reciprocate under the action of the water relative to the fixed piston.

Our EP-A-0384690 discloses a tank washer comprising a piston immovably connected, in operation, to liquid supply means, a body reciprocally surrounding the piston and at least one liquid ejection nozzle oscillatably connected to the body, and a valve mechanism operable by the oscillation of the at least one nozzle to index the body around the axis.

Preferably, in such an arrangement, the axis about which the nozzle or nozzles is/are indexed, during operation, substantially corresponds to the longitudinal axis of the tank washer. Preferably the axis about which the or each nozzle operates during operation of the tank washer is afforded by a nozzle tube contained in a transverse hole formed in the main body of the tank washer, with the nozzle tube which, during operation, oscillates the or each nozzle being connected to the reciprocable main body by a coupling piece. A preferred arrangement is that wherein the main body reciprocates relative to a piston occupying a fixed position relative to a tank which is to be cleaned, and wherein reciprocation of the main body is brought about by applying liquid pressure successively to the opposite sides of the piston.

In such an arrangement as disclosed in EP-A0384690, preferably a pivotally mounted valve is provided by which liquid is fed successively to the opposite sides of the piston, bleed holes being provided adjacent each side of the piston for the exhaust of liquid from that region when the latter is not subject to liquid pressure, each bleed hole being smaller in size than is the liquid supply conduit to the region that is being drained by the corresponding bleed hole. In the arrangement described and illustrated in EP-A-0384690 the valve is loaded by the storage of energy in at least one spring and is subsequently triggered to move independently of the action that causes the triggering by releasing the at least one spring.As is acknowledged in EP-A-0384690, it is a characteristic of reciprocating pistons that are operated by water or aqueous solution that the piston itself cannot be used to switch the valve directly at the end of its stroke to reverse the direction of flow. The reason for this is that, as soon as the valve is moved even a small amount, the action "locks" and no further movement takes place. It is necessary that the valve should receive from the piston some energy and should store that energy and that it is then triggered so that it will move independently of the action that initiates the triggering. This is known as a "load and fire" mechanism.

It is with a mechanism of the "load and fire" type that the present invention is concerned.

According to the present invention, there is provided a piston and cylinder arrangement with provision for reversing the direction of relative movement between the piston and the cylinder, by feeding-a fluid under pressure through fluid supply means successively to opposite sides of the piston, there being first and second zones of variable volume on opposite sides of the piston, the zones being defined by the piston and cylinder, and there being bleed holes associated respectively with the first and second zones, wherein the piston head is hollow to provide a chamber which is in communication with the fluid supply means, the piston head being provided with a first bore providing communication between the chamber and the first zone and a second bore providing communication between the chamber and the second zone, the first and second bores having valve seats on their end regions facing the chamber and being larger than the bleed holes in the first and second zones, there also being provided in the chamber a resiliently flexible valve member capable in one region of successively abutting the first and second valve seats so as successively to block off the first and second bores respectively, as well as an elongate element for carrying the valve member at an other of its regions, the elongate element having first and second end regions capable of projecting through the opposing faces of the piston head into the first and second zones respectively and being movable in the longitudinal direction relative to the piston head, the arrangement being such that, in use, with fluid being supplied under pressure to the chamber through the fluid supply means and with the valve member abutting the first or second valve seat, fluid passes through the second or first bore into the second or first zone which causes relative movement between the piston and cylinder and an increase in volume of the second or first zone, until the first or second end region of the elongate element abuts the adjacent end face of the cylinder and causes the elongate element to move relative to the piston head as the piston head continues to move, until such time as the one end region of the valve member, in view of its resiliently flexible nature, springs across to the second or first valve member, whereupon relative movement between the piston and cylinder in the opposite direction is initiated.

Conveniently the bleed holes are arranged in the cylinder wall just beyond the positions of maximum travel of the piston head relative to the cylinder, although it would be possible for the bleed holes to be arranged in the piston provided that the bleed holes and any outlet ducts leading therefrom were kept separate from the fluid supply means.

The most convenient arrangement is for the piston rod to be hollow and to communicate directly with the chamber within the piston head.

The valve member can take the form of a thin strip of spring steel but other materials could be employed provided that the material is resiliently flexible. It is the resilient nature of the valve member which allows it to store some energy so that when triggered, it can move independently of the action that initiates the triggering, on the "load and fire" principle.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 is a vertical section through one embodiment of a piston and cylinder arrangement in accordance with the present invention; Figure 2 is a perspective view from above of the valve member and associated elongate element forming part of the arrangement of Figure 1; and Figure 3 is a vertical section through the valve member and associated elongate element showing the valve member bowing towards one of the valve seats.

Referring firstly to Figure 1, there is shown a piston 1 which is fixed and is intended to remain stationary. The piston 1 has a hollow piston rod 2 which communicates at one end 3 to a source of fluid, usually water, under pressure, and at the other end the piston rod is secured to a piston head 4 which is provided with a hollow chamber 5 which is in communication with the interior of the hollow piston rod 2. Intended for reciprocating movement with respect to the piston 1 is a cylinder 6 which has a cylindrical side wall 7, a closed end wall 8 and at the opposite end another end wall 9 which is provided with a central aperture 10 in which the piston rod 2 is sealingly located, there being provision for the cylinder 6 to move freely with respect to the fixed piston 1.

In the cylindrical side wall 7 near the first closed end wall 8 is a first bleed hole 11, and also in the cylindrical side wall 7 but near the other end wall 9 is a second bleed hole 12. Defined by the piston head 4, the closed end wall 8 and that part of the cylindrical side wall 7 adjacent the end wall 8 is a first zone 13. On the opposite side of the piston head 4 is an annular second zone 14 defined by the other end wall 9 and the adjacent region of the cylindrical side wall 7, the piston rod 2 and the piston head 4. The zones 13 and 14 together constitute a fixed volume but each zone is variable in volume depending upon the relative position of the piston 1 with respect to the cylinder 6.

Located within the chamber 5 of the piston head 4 is a first valve seat 15 which is provided with a first bore (not numbered) which is capable of providing communication between the chamber 5 and the first zone 13. Opposite the first valve seat 15 and still within the chamber 5 is a second valve seat 16 provided with a second bore 17 which is capable of providing communication between the chamber 5 and the second zone 14. The first bore and the second bore 17 are larger in cross-sectional area than the first bleed hole 11 and second bleed hole 12 respectively, with the result that when fluid is introduced through the piston rod 2 into the chamber 5 it can flow through the first bore or second bore 17 into the first zone 13 or second zone 14 at a rate greater than that at which it can escape through the first bleed hole 11 or the second bleed hole 12.As a consequence, as the volume of water builds up in the first zone 13 or second zone 14, relative movement between the cylinder 6 and the piston 1 is caused.

Located wholly within the chamber 5 is a valve member 18 which is formed of a resiliently flexible material and which at one end region 19 is capable of abutting the first valve seat 15 or the second valve seat 16 so as to close off the first bore or the second bore 17, respectively. The valve member 18 is fixedly secured at another end region 20 to an elongate element 21 which extends generally perpendicularly with respect to the valve member 18. The elongate element 21 at a first end region 22 projects through a hole in the piston head 4 and into the first zone 13, and at its second end region 23 projects through an opposing hole in the piston head 4 and into the second zone 14.

The first end region 22 of the elongate element 21 is capable, when there is sufficient relative movement between the piston 1 and the cylinder 6, of abutting the closed end wall 8 of the cylinder 6 so as to cause, during continued relative movement between the piston 1 and the cylinder 6, movement of the elongate element 21 relative to the piston head 4. Similarly, the second end region 23 of the elongate element 21 is capable, when there is relative movement between the piston 1 and cylinder 6 in the opposite direction, of abutting the end wall 9 of the cylinder 6 and is capable, during such continued further movement in that opposite direction, of causing relative movement between the elongate element 21 and the piston head 4.Movement of the element 21 relative to the piston head 26 also causes correponding movement of the valve member 18 at least initially in the other end region 20 of the valve member 18.

Having described the constructional features associated with the piston and valve arrangement shown in the drawings, the operation of that arrangement will now be described. Fluid under pressure, usually water under pressure, is fed via the one end 3 of the piston rod 2 to the chamber 5 within the piston head 4. Let us assume that the elongate element is positioned such that the amount of first end region 22 projecting into the first zone 13 is the same as the amount of second end region 23 projecting into the second zone 14 and that the valve member is currently rectilinear with its one end region positioned mid-way between the first and second valve seats 15 and 16. The water entering the chamber 5 will leave the chamber 5 by both the first bore and second bore 17.However, as the valve member is flexible it will, after a short while, certainly be moved by the movement of water to one of the two valve seats 15, 16 and be forced into a firm fit with that valve seat thereby closing the respective bore. By analogy, it is rather similar to a bath plug which, when lifted to release the bath water, will slam back into place if allowed near the plug hole. Let us assume that, as shown here, the valve member 18 moves upwardly to abut the valve seat 16 thereby closing off the second bore 17. Water which continues to flow into the chamber 5 will leave the chamber 5 through the first bore in the first valve seat 15 and will enter the zone 13.

Although a certain amount of the water entering the zone 13 will be lost through the first bleed hole 11 there will be a net build up of water in the first zone 13 with the result that, bearing in mind that the piston 1 is fixed, the cylinder 6 is urged downwards (in Figure 1), with any water or air in the second zone 14 being allowed to exhaust through the second bleed hole 12. This downward movement of the cylinder continues and, in due course, the second end region 23 of the elongate element 21 abuts the end wall 9 and, with continuing downward movement of the cylinder 6, causes the elongate element 21 to be moved downwardly relative to the piston head 4.

For a while, even though the elongate element 21 is being moved downwardly relative to the piston head 4, the one end region 19 of the valve member 18 remains firmly pressed against the second valve seat 16, with the valve member being now bowed, as is clearly seen in Figure 3. The one end region 19 of the valve member 18 remains in contact with the seat 16 in view of the pressure of water on that face of the valve member opposite to the face abutting the second seat 16.

A stage will be reached, however, at which the force causing the valve member 18 to bow will overcome the pressure keeping the one end region 19 of the valve member 18 against the second valve seat 16, whereupon the valve member 18 will spring away from the second valve seat 16 and go straight to the first valve seat 15, and the water pressure within chamber 5 will now "lock" the valve member 18 onto the first valve seat 15, with consequent blocking of the first bore provided within the first valve seat 15. With water continuing to be introduced into the chamber 5 from the source via the piston rod 2, the water will now leave the chamber 5 via the second bore 17 in the second seat 16 and thus be introduced into the zone 14, which causes the cylinder 6 to move upwardly relative to the piston 1, thus reversing the direction of travel of the cylinder 6.

It is to be appreciated that the "loading" of the valve member 18 is achieved by the bowing of the resilient spring material of the valve member 18. The "triggering" occurs as the valve member 18 leaves one valve seat and moves to the other. The action is intermittently continuous and is simple.

To assist in understanding the action of the valve, it is worth again considering the anology with the bath plug. Imagine that a tension spring held at one end in a hand and is attached at the other end to a bath plug, and the bath is filled with water. If then an attempt is made to remove the plug by gradually pulling on the spring in a direction away from the plug hole, the plug will not at first be removed from the plug hole because of the water pressure holding the plug in place. As the spring is extended, it will store energy until the point is reached at which the force stored in the spring is greater than the hydraulic pressure holding the plug in the plug hole, whereupon the plug will jump away from the plug hole, moving independently of the slow hand action which is lifting the spring. This is how the "load and fire" action is effected.

It can readily be appreciated how the piston and cylinder arrangement of the present invention and in particular the embodiment illustrated in the accompanying drawings can be incorporated in a tank washer of the type disclosed in EP-A-0384690, in place of the pivotally mounted valve arrangement disclosed in that specification. For the sake of brevity, there are not provided drawings showing a tank washer with the piston and cylinder arrangement in accordance with the present invention, as it is perfectly clear how the arrangement of the present invention can be substituted for the arrangement disclosed in EP-A-0384690.

Claims (6)

1. A piston and cylinder arrangement with provision for reversing the direction of relative movement between the piston and the cylinder, by feeding a fluid under pressure through fluid supply means successively to opposite sides of the piston, there being first and second zones of variable volume on opposite sides of the head of the piston, the zones being defined by the piston and cylinder, and there being bleed holes associated respectively with the first and second zones, wherein the piston head is hollow to provide a chamber which is in communication with the fluid supply means, the piston head being provided with a first bore providing communication between the chamber and the first zone and a second bore providing communication between the chamber and the second zone, the first and second bores having valve seats on their end regions facing the chamber and being larger than the bleed holes in the first and second zones, there also being provided in the chamber a resiliently flexible valve member capable in one region of successively abutting the first and second valve seats so as successively to block off the first and second bores respectively, as well as an elongate element for carrying the valve member at an other of its regions, the elongate element having first and second end regions capable of projecting through the opposing faces of the piston head into the first and second zones respectively and being movable in the longitudinal direction relative to the piston head, the arrangement being such that, in use, with fluid being supplied under pressure to the chamber through the fluid supply means and with the valve member abutting the first or second valve seat, fluid passes through the second or first bore into the second or first zone which causes relative movement between the piston and cylinder and an increase in volume of the second or first zone, until the first or second end region of the elongate element abuts the adjacent end face of the cylinder and causes the elongate element to move relative to the piston head as the piston head continues to move, until such time as the one end region of the valve member, in view of its resiliently flexible nature, springs across to the second or first valve seat, whereupon relative movement between the piston and cylinder in the opposite direction is initiated.

2. An arrangement according to claim 1, wherein the bleed holes are arranged in the cylinder wall just beyond the positions of the maximum travel of the piston head relative to the cylinder.

3. An arrangement according to claim 1 or 2, wherein the piston rod is hollow and communicates directly with the chamber within the piston head.

4. An arrangement according to claim 1, 2 or 3, wherein the valve member is in the form of a thin strip of spring steel.

5. An arrangement according to claim 1, substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

6. A tank washer which includes an arrangement as claimed in any preceding claim.